Solar PV Peak Output?

wensleydale

Thanks guys- if it's any help they are REC 240W panels so 30V each is right.

Based on this it's sounding as if it is actually ok, but the output is much less than I expected- not ideal....

Martyn1981

Rich, me again.

Didn't explain the MPPT thingie.

Unless your panels are all on the same orientation, roof slope, same panel models etc, you really need 1 MPPT per 'system'.

Your roofs being so different SE / SW, need an MPPT each. So either 2 inverters, or a 'clever' inverter that has dual MPPT's, which will treat your install as 2 systems.

SB1200's are cheaper than your SB2500HF, but 2 would cost more. The SB3000TL is a more efficient model than the HF's as they have 'OptiTrack Global Peak', however I've just looked it up and it's only got 1 MPPT.

Staying within the SMA range, the next bet might be the SB3600TL, probably several hundred pounds more than the 2500HF, but less than 2 1200's. It's a very efficient model, dual MPPT and has the better tracking of the TL range. I've only mentioned the money so you are better informed, obviously this shouldn't be a concern to you as the installers should have been aware of this when they quoted you for an 'optimised working system'.

Sorry I don't know much about other makes and models of dual MPPT inverters (but happy to look).

Ask your installers if the 3600 is suitable, and if the voltage minimum is ok. I think the 5 panel 'system' would be ok, but at this point I've run out of talent!!!

Hope this helps.

Mart.

PS spec sheet on 3600

http://www.naturalsparx.co.uk/media/pdfs/SM01_Sunny_Boy_TL_3600_Inverter_Technical.pdf

grahamc2003

wensleydale wrote: »

Hi all,
I've been out this morning and looked at the software readings but to be honest I am not sure what I need to look for- I've taken screen grabs of what I think are the right pages and saved them on the links below- can anyone offer any suggestions?

http://www.londonweddingdisco.co.uk/screengrab.xlsx

http://www.londonweddingdisco.co.uk/screengrab2.xlsx

Thanks
Rich

I'd forget about all that - you have found your problem. A single mppt will set the incorrect max power voltage for your set up (that is, some panles facing SE and some faving SW with a single mppt). Simply having dual strings isn't tha important factor, the dual mppt is.

The tracker works by varying the voltage and noting the change in power. It effectively differentiates the voltage/power curve, and finds the point where the differential is zero and asusmed that's the maximum power.

That is fine if the volatge power curve of the panels on the two strings has a single maximum (as they would if the orientation of both strings were identical). In your setup, the voltage/power curve will have several peaks or local maxima. Most inverter software simply detects the first local maximum, and sets the voltage to that. In your setup, that voltage will usually be a long way off the true max power voltage. Around midday, the panels will have a single maximum which the inverter will detect, so you should be getting the real max power from your panels around that time. Away from lunchtime, your sun facing panels will have their voltage set accoring to the sunstarved panels, and the result is your output will be very low. Some inverters claim to have a single mppt which searches all local maxima and sets the voltage to the highest of those to alleviate this problem - not sure hoiw they work in practice. I would say it's a definate design error having a single tracker on your system, and would get them to put a dual tracker inverter in.

jamesingram

Rich ,
Get in touch withyour installers and get them to explain the set up .
It appear from whats been said , the set up has not been designed correctly, in fact rather poorly .
You've definatley only got one string and your inverter only has one MPP tracker , so 2 strings would make no difference anyway.
As mentioned by other , all panels on each MPPT should really have the same orientation and declination .
what you really need is a inverter with a dual tracker or 2 inverters for a dual orientation system.

edit : looks like most here agree. poor design setup.

Martyn1981

seagull09 wrote: »

That's exactly the problem I've got, unfortunately. But because only 4 panels are facing other direction (and no room for more) it's not enough to operate one of a dual MPPT inverter, so I'm probably going to have to go down the Micro Inverter route. Or remove the 4 panels altogether, rather reluctant to do that though.

Hiya Seagull, hope you're getting a sunny day like me today.

If you read through the 'so now I've got .....' thread, you'll see EdWink had the very same issue, 10 panels, same orientation, but 6 at 30deg pitch, and 4 at 20 deg, plus differing shading. Total too small for a dual, and the 4 panels too small for a SB1200.

She's had it changed, and the 4 panels connected 2 each to 2 Steca 500 inverters. We were hogging the thread a bit, so the end of the discussion moved to PM's, but I don't think she'll mind me saying that generation looks good so far since the change, but it is early days.

Mart.

EricMears

wensleydale wrote: »

Thanks for this- without sounding like too much of a novice how can I confirm the single/dual string- follow the cables and look for what?
There are 2 inputs into the inverter but I guess I need to see how they are connected to the panels?

Regardless of how many strings such an inverter might support, your screen dump shows pretty conclusively that it's only actually using one string - which (as Martyn has pointed out) would need two cables entering the inverter box. Even if you have 4 cables (two from SE & 2 more from SW) it would seem that they're joined inside the terminal box rather than feding two separate parts of the circuitry.

Afraid Martyn is also guilty of one of those 'errors' to which our forum seems to be prone. I'm absolutely not an 'expert' nor do I understand it any better than he does :rotfl::rotfl::rotfl::rotfl:

I am however quite happy with looking at Sunny Explorer output windows - hardly an hour goes by when I'm not viewing mine:eek:


My limited expertise is sufficient to agree with the other posters who have pointed out that to host two separate installations pointing in different directions on the same string is a recipe for disaster.

Afraid my 'expertise' isn't even sufficient to differentiate between a string and an MPPT. I'd always thought of them as equivalent terms. OMG - another 'error' !

grahamc2003

seagull09 wrote: »

That's exactly the problem I've got, unfortunately. But because only 4 panels are facing other direction (and no room for more) it's not enough to operate one of a dual MPPT inverter, so I'm probably going to have to go down the Micro Inverter route. Or remove the 4 panels altogether, rather reluctant to do that though.

Ha! I had exactly the same type of thing. Just before the March cutoff, I had a local installer quickly spec up a system on my se/sw roof. Accpeted the quote (it was cheap - for a breif period they had 10% off their already low prices) but then their tech guys refused the design, and they offered me a smaller system just facing SW. I didn't really understand at the time why they were turning away business. They just said they couldn't get a uitable inverter. I asked about micro inverters but they didn't like those - more things to go wrong. So I accepted the smaller system - and it looks like their tech guys were perfectly correct.

Mines working fine, better than expected. A tiny amount of shading really knocks the output, and I have a tree which is getting the chop next week so will improve things a lot. Even the scaffolding poles cut the output a lot, and when that was taken down, the output improved noticably. The effect of shading is minimal if you have microinverters, so getting microinverters may solve your current problem and also any shading issues you might have.

EricMears

grahamc2003 wrote: »

So I accepted the smaller system - and it looks like their tech guys were perfectly correct.

Sounds like a great example of a conscientious contractor ! Alas, we can't say the same for Wensleydale's lot ! Perhaps just as well he retained part of fee.

Hobbo2006

jamesingram wrote: »

i live close to you and our 4.32kW of panels (SE). gen. 18.77kWh today
max single point output approx 3kW
11 and 5 on each orientation/string sounds a strange setup , what was the reasoning behind this from the installers ?

Well they couldn't fit them all on one side and the east side has chimney, boiler vent and soil vent so less roof space and more shading.

As it stands I think shading is not as big a problem as they make out.

Numbnuts

EricMears wrote: »

It would indeed be simple to add a few more panels. However, that would drop you into the next FIT band and indeed it would probably 'expel' you from the old scheme altogether.

My installation is far from 'perfect' - it's been put a high as possible to avoid shading from nearby trees so is on top of a very shallow dormer roof. Even on Summer Solstice day I won't quite get to optimum angle but I am fairly confident of getting to 4kw. I peaked at well over 3.5kw in late August so should get to same sort of peak next month and hopefully better still during good days in May, June & July (if we have any !:mad:).

A near neighbour has a similar set of panels but on tracking frames. Even his isn't 'ideal' as there is some tree shading early and late in day.

This is not the case !!!

example 18 x 250w panels = 4.5kwp system

which is declared installed capacity

but if you used a inverter say a sma 4000TL set to g83

which would mean the declared net capacity to be 3.68kwp

there you would claim the higher fits !!!!

as the FITS providers band system from the net capacity in terms of FITS payment.

the system is capped and would not exceed 3.68kwp but would reach 3.68kwp quicker and more often on cloudy days etc.

BUT i have never tried this method with any installs as it would be a risk say if the FITS provider gets funny.